1. Field of the Invention
The present invention relates to semiconductor devices and manufacturing methods therefor. More particularly, the invention relates to semiconductor devices in which a semiconductor element is hermetically sealed within an enclosure formed by a package case and a cap (or a package lid) that are bonded together using a bonding/sealing wire, and also relates to methods for manufacturing such semiconductor devices.
2. Background Art
A semiconductor element might be physically damaged or its characteristics might be degraded if it is exposed to moisture, contamination, heat, electromagnetic field, etc. To prevent this, semiconductor elements such as high frequency and optical modules need be hermetically sealed and protected from such environmental effects. A common way to hermetically seal a semiconductor element is to mount it in a package case and bond a cap to the package case. At that time, the cap and the package case must be seamlessly bonded together to achieve hermetic sealing.
JPA-08-227946 (1996) also discloses a semiconductor device in which a semiconductor element is hermetically sealed within an enclosure formed by a package case and a cap that are bonded together. To allow the cap to be reliably bonded to the package case, the portion of the cap to be in contact with the package case has a protrusion, and the mating portion of the package case has a groove structure to receive that protrusion. The package case and the cap are bonded together at low temperature by causing the protrusion of the cap to contact and engage the groove structure of the package case and then applying ultrasonic vibration to the cap while pressing the cap and the package case together and holding the package case against movement.
The method for bonding a cap to a package case disclosed in the above-mentioned patent publication requires forming a protrusion on the cap and forming a groove structure on the package case. JP-A-2006-121109 discloses an exemplary method for forming a protrusion on a wafer (or cap). Specifically, after forming a film on the wafer in the wafer manufacturing process, portions of the surface of the wafer are selectively removed to form a protrusion. This additional manufacturing process allows for reliable bonding between the package case and the cap, but prevents reductions in the cost of the semiconductor device. It should be noted that other prior art includes JP-A Nos. 2003-152131, 2002-208650, 2002-118193, and 6-188672 (1994).